This invention relates generally to microwave and millimeter wave (mm-wave) radio frequency (RF) circuits, and more particularly to terminations for transmission line and one-sided matching to include wire bond inductances.
It is well known that an impedance change can cause signal reflection in high speed circuits. The reflection coefficient is given by:                     Γ        =                                            Z              L                        -                          Z              o                                                          Z              L                        +                          Z              o                                                          (                  eq          .                                           ⁢          1                )            where ZL is the load impedance and Zo is the transmission line characteristic impedance. When transmission lines end in an open circuit, ZL is infinity. As a result Γ is one and the signal is entirely reflected back. It is therefore important to provide a match termination to reduce reflection and signal bounce in many high speed circuits such as hybrid couplers, T/R modules, circulators, power combiners, absorptive filters, doublers, mixers couplers and so on. In addition, a typical high frequency switch-matrix used for optical signal routing has N by N lines crossing each other and going to the edge of the chip. Each of the line ends need termination. Thus a total of N2 terminations are required. Since the switch-matrixes are made on an expensive substrate such as Indium Phosphide (InP) or Gallium Arsenide (GaAs) to allow high frequency signal processing, it may be desirable to terminate these transmission lines in their characteristic impedance outside the integrate circuit (IC). Often the terminations need to absorb 1-5 W of power and have broadband width (e.g., DC-to-40 GHz).
Since high power terminations require large chip area and are built on thermally conductive substrates such as Aluminum Nitride (AlN) and Beryllium Oxide (BeO), they are often included outside the expensive InP or GaAs chip. Moreover, a single bond-wire is often desirable as it is compatible for large-scale manufacturing. The bond wire is electrically represented by an equivalent circuit that usually comprises of a reactance matrix comprising of shunt capacitance followed by a series inductance and another shunt capacitance. The reactance matrix is dominated by the series inductance.